How to invoke a Data Mapper? Is persistence layer a dependency of Data Mapper?

Data Mapper is a layer of separation between domain and persistence layers. The following are facts (unless I misunderstand):

• domain layer is ignorant of persistence layer
• persistence layer is ignorant of domain layer
• both domain and persistence layers are ignorant of Data Mapper.

All that said, please find my questions below.

• How to invoke a Data Mapper if the domain layer has to be ignorant of it?
• Is persistence layer a dependency of Data Mapper?

Thanks